Which of the following sentences contains a compound predicate?
a. she placed the shells in a plastic bag while he dried himself off.
b. she washed the shells and dried them in the sun.
c. she raced along the path to beat him to the beach.
d. while he swam, she collected shells.

B.

Explanation:

Compound predicates are the ones in which two or more verbs have a common subject. In other words, a compound predicate is formed when in a sentence two or more actions are shared or done by the same subject and these two verbs are connected by a conjunction.

From the given options, the sentence that contains a compound predicate is in the option B.

In option B, two verbs are "washed" and "dried" and the same subject is "She" and the two verbs are connected with a conjunction "and".

So, option B contains compound predicate as it contains two verbs connected with a conjunction shared by the same subject.